1. Field of the Invention
This invention relates to an apparatus for making a nonwoven web, comprising a carding drum, a continuously movable, air-permeable collecting surface member, which is arranged to collect the fibers which have been discharged from the carding drum and are entrained by an entraining air stream, a suction box, which adjoins the collecting surface member on that side thereof which is opposite to the carding drum, and a suction duct, which extends between the carding drum and the collecting surface member and adjoins the carding drum at a peripheral portion thereof which is directly opposite to the collecting surface member, wherein air supply passages for supplying air to the suction duct are provided throughout a predetermined working width of said drum and disposed adjacent to said duct at leading and trailing boundary means thereof with respect to the sense of rotation of the carding drum.
2. Description of the Prior Art
Because in apparatuses of that kind the suction duct is disposed between the collecting surface member and a peripheral portion thereof which is directly opposite to the collecting surface member, the length of that suction duct and also the length of the flight path of the fibers can be selected as required in each case, independently of the diameter of the drum. As a result, the average length of the flight path of the fibers may be restricted to an extent which is smaller than the radius of the drum so that the risk of a formation of fiber lumps is greatly reduced. But that result cannot be achieved unless the singled fibers are uniformly detached from the carding drum and the fibers are conveyed within the suction duct without a disturbance. The conditions of flow within the suction duct may properly be influenced by the provision of air supply passages in the region in which the carding drum is adjoined by those boundary means of the suction duct which are the leading and trailing boundary means with respect to the direction of rotation of the carding drum. But the fibers may not sufficiently uniformly separate from the carding drum and in that case the fibers will not be uniformly deposited on the collecting surface member in spite of the existence of desirable 20 conditions of flow within the suction duct.